Shock absorbers are used in connection with automotive suspension systems and other suspension systems to absorb unwanted vibrations which occur during movement of the suspension system. In order to absorb this unwanted vibration, automotive shock absorbers are generally connected between the sprung mass (the body) and unsprung mass (the suspension) of the automobile.
The most common type of shock absorber in automobiles is the dashpot type in which a piston is located within a pressure tube. The piston is connected to the sprung mass of the vehicle through a piston rod. The piston divides the pressure tube into an upper working chamber and a lower working chamber, both of which are filled with a damping fluid. Because the piston, through valving, has the ability to limit the flow of the damping fluid between the upper and lower working chambers within the pressure tube when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung mass to the sprung mass. In a dual tube shock absorber, a fluid reservoir is defined between the pressure tube and the reserve tube. A base valve is located between the lower working chamber and the fluid reservoir to produce a damping force which also counteracts the vibration which would otherwise be transmitted from the unsprung mass to the sprung mass of the automobile.
Automotive shock absorbers are generally provided with bleed orifices which allow the restricted flow of damping fluid from the upper side of the piston, which is know as the rebound side, to the lower side of the piston, which is known as the compression side. These bleed orifices provide the shock absorber with a portion of its damping characteristic. Automotive shock absorbers also may include a blow off valve of some type. The blow off valve is normally in a closed position. However, when fluid pressure within the pressure cylinder reaches a predetermined level, the blow off valve opens reducing considerably the restriction of damping fluid flow between the two sides of the piston.
Various designs in the prior art combine the conventional piston valving with a blow off valve. For example, U.S. Pat. No. 4,721,130, issued on Jan. 26, 1988 to Hayashi for “Valve Structure of Hydraulic Buffer,” discloses a valve structure used in a hydraulic buffer. A valve body is used for opening and closing ports in the piston. As the piston rod is extended, a free end of the valve body deflects about a first fulcrum point to allow fluid to pass. When the piston is moving at a high rate of speed and the force of the fluid passing through the port exceeds the pre-load set by the spring, the spring seat is depressed so that more fluid flows through the port while deflecting the valve body about a second fulcrum point.
Additionally, U.S. Pat. No. 2,717,058, issued to Brundreit on Sep. 6, 1955 for “Shock Absorber Control Valve,” discloses a shock absorber control valve for controlling restricted flow of hydraulic fluid between opposite ends of a pressure tube. A valve disk flexes upwardly against a rigid retainer plate as permitted by the angularity of the face portion of the plate. As the requirement for fluid flow increases, the valve member and the retainer are moved against the compression spring to change the fluid flow rate.
While these prior art systems have performed acceptably, they are relatively complex and they fail to produce optimum results in the terms of efficiency and cost. The continued development of shock absorbers includes the development of systems which combine the flexing disk function of a rebound valve with the blow off function in a system that is less complex and less expensive while providing the necessary damping acquirements.